Because two-way video communications can give telephone users the added ability to communicate graphical information and to see facial expressions and gestures that cannot be conveyed by audio alone, much emphasis has been placed on commercial development of such systems. For example, at the 1963 World's Fair in New York City, AT&T demonstrated a prototype of its Picturephone video telephone system, by which panics at remote locations could see and speak with each other. Unfortunately, the Picturephone system was too costly, and its picture quality was not good enough for commercial deployment at that time. In recent years, video telephones that work with analog telephone lines have been demonstrated. However, due to the limited bandwidth (.sup..about. 3 KHz) of conventional telephone lines, and the consequent limitation on the amount of audio and video information that can be carried through the analog telephone network, commercial development has again been limited, such that most products in this category offer the ability to see only limited motion (a few black- and-white frames per minute) on a relatively small display with poor resolution.
In order to overcome the bandwidth limitation associated with video telephony transmitted over the analog telephone access network, video telephones more recently have been designed to work with digital telephone access networks, such as ISDN. However, at the present time, digital access facilities to consumer homes are not readily available.
Still other video telephone systems have been designed to overcome the access, bandwidth and cost problems, but each suffers some drawbacks. For example, many systems are point to point, connecting, for example, individual classrooms in a campus environment or video-teleconference rooms in a corporate environment Thus, users in off-net locations cannot be served. Some other systems provide local video telephone service to only a small group of users. For example, in U.S. Pat. No. 4,847,829 issued to E. Neil Tompkins et al. on Jul. 11, 1989, analog video terminals are connected to a centrally located analog video switch via dedicated coaxial cables in a star configuration. The number of users is limited by the capacity of the video switch. This approach is also not economical for serving a mass consumer market because each video terminal requires a dedicated coaxial cable to access the video switch.
U.S. Pat. 4,901,367 issued to Victor Nicholson on Feb. 13, 1990, describes a coaxial cable network operating at 800 MHz that is shared by sixty (60) users, each assigned a dedicated 12 MHz bandwidth. However, the patented system does not provide for communication with other stations not connected to the same coaxial cable, and indeed, sharing by only sixty users is still not economical enough.
U.S. Pat. 4,686,667 issued to Horst Ohnsorge on Aug. 11, 1987, describes an all-digital broadband subscriber loop system that uses a high-speed digital central switch fed by multiple optical fiber links, each operating at 1.12 Gb/s. The 1.12 Gb/s bandwidth is divided into sixteen 70 mb/s channels which are then carried by dedicated coaxial cables to subscribers' premises in a star configuration. The drawback of this system is that each subscriber has to incur the heavy cost of a video codec to digitize audio and video signals, the cost for multiple levels of digital multiplexing, and the cost of dedicated co-axial cable for access.
Other systems use optical fiber to directly link to subscriber homes in order to obtain the high bandwidth needed for full motion video. However, these facilities are expensive, and thus are not accessible to the ordinary household. Besides, it will take decades to reach ubiquity.
In recent years, a number of developments have converged that could make video telephony readily available to a large number of users at a relatively reasonable cost. The present invention takes advantage of these developments. Specifically, in 1990, an international video compression standard (CCITT H.261) became available which describes digitization and compression of analog video signals at rates which are multiples of 64 Kb/s (i.e., 1.times.64 Kb/s to 30.times.64 Kb/s ). These codecs will be widely available, and if they can be shared by multiple users, the per user cost will be readily affordable. With respect to interconnecting video telephone signals among geographically distant locations, a switched digital telephone network capable of providing capacity in multiples of 64 Kb/s is now available from interexchange carriers such as AT&T. With respect to distribution of video telephone signals to video telephone subscribers, the cable TV industry deployed coaxial distribution networks to about 90 percent of all U.S. households. Since cable networks in general carry some 20 to 80 downstream channels, the cost of dedicating several downstream channels for video telephony in a cable network is relatively inexpensive, because these channels can be shared by a large number of households. In the coaxial network, the 5-30 MHz bandwidth is typically reserved for upstream channels (from the subscriber premises to "head end" apparatus maintained by the cable provider) that currently have little usage, either for passive pay-per-view messages or for local program generation. These upstream channels can be used to transmit upstream video telephone traffic. Besides, the cable TV industry also has a well-publicized evolution plan to deploy fiber trunks to bring high quality signals from the head end to hubs for local distribution. When this happens, head end equipment will be duplicated for each new hub, thereby subdividing a large cable network into multiple smaller networks, each operating an "independent" distribution network. This approach will reduce the number of households sharing the coaxial cable distribution network associated with one fiber hub area. Thus, the upstream and downstream channels dedicated to video telephony in a particular cable network can be shared by a manageably small group of users.
With respect to origination and termination equipment, 12 million camcorders have already been sold in the U.S., and the growth rate is projected to be 20 percent annually. These camcorders can be used as origination equipment for video telephony. Termination equipment can be an ordinary television set. At the user premises, only inexpensive network interface equipment is required to access the coaxial cable facility.